194 ACTION OF THE VALVES OF THE MAMMALIAN HEART. 



Prevention of Occlusion of Aortic Orifice. 



The manner in which the anterior cusp of the mitral valve, from its obliquity and 

 connection with the membranous septum between the aorta and the auriculo-ventricular 

 opening on the one hand, and the papillary muscles on the other, assists in preventing 

 the occlusion of the aortic orifice, has been described on p. 187. 



EXPLANATION OF PLATES. 



Plate I. 



Fig. 1. Transverse section through middle third of ventricles of human heart (rigor-mortis) to show relation- 

 ship of cavities, and bulging of septum into right ventricle, b, anterior papillary muscle of right 

 ventricle ; c, posterior papillary muscle of right ventricle ; d, anterior papillary muscle of left 

 ventricle ; e, posterior papillary muscle of left ventricle. Natural size. 



Fig. 2. Transverse section through lower third of ventricles of human heart (relaxed) to show trabecular 

 structure at apex of right ventricle, with origin of papillary muscles, b anterior, and c posterior; 

 a anterior, and e posterior, papillary muscles of left ventricle. \\ natural size. 



Fig. 3. Transverse section through upper third of ventricles of human heart (relaxed), looking upwards, to 

 show relationship of pulmonary orifice, conus, and right auriculo-ventricular orifice with tricuspid 

 valve, a superior, b anterior, and c posterior papillary muscles; d infundibular, e posterior, 

 and / internal cusps of valve. Note greater thickness of ventricular wall laterally than in front. 

 On left side mitral valve x situated behind and to the left. 1^ natural size. 



Fig. 4. Right ventricle of rabbit's heart to show papillary muscles taking origin from septum. Natural size. 



Fig. 5. View of ventricles from above (heart of child), auricles removed. Shows planes of section to de- 

 monstrate mitral (B) and tricuspid (A) valves. Natural size. 



Fig. 6. Right ventricle of heart of adult man, to show stretching of infundibular cusp of valve, between 

 superior and anterior papillary muscles. Letters as in 3. About \ natural size. 



Plate II. 



Fig. 7. Vertical transverse section of adult human heart in diastole (looking backwards), to show position 

 of tricuspid valve, t, trabecular structure at apex of ventricle from which papillary muscles 

 rise ; b, anterior muscle ; d, infundibular cusp of valve ; h, internal cusp ; v, posterior wall of 

 left ventricle. \ natural size. 



Fig. 8. Vertical antero-posterior section of left ventricle of adult human heart in diastole (in line B, fig. 

 4), looking to left, b, anterior cusp of mitral valve ; a, posterior cusp somewhat displaced from 

 its position against the posterior wall of the ventricle ; d, anterior papillary muscle ; au, left 

 auricle; as, aorta; rv, conus of right ventricle; c, muscular cushion under right anterior cusp 

 of aortic valve \ natural size. 



Fig. 9. Vertical antero-posterior section of heart of sheep (somewhat more antero-posterior than 8). Heart 

 in semi-rigor — letters as in 8. I, posterior papillary muscle, \ natural size. 



Fig. 10. Vertical transverse section of heart of rabbit fixed in the first stsge of ventricular systole, to show 

 mode of closure of tricuspid valve. /, internal cusp applied to septum ; d, external cusp drawn 

 in upon septum ; p, papillary muscle. (From a drawing.) Natural size. 



Fig. 11. Vertical antero-posterior section of heart of rabbit in first stage of ventricular systole, blood removed 

 from left ventricle. Shows application of anterior and posterior cusps of mitral valve to occlude 

 auriculo-ventricular orifice, ao, aorta; au, left auricle; ac, anterior mitral cusp ; pc, posterior 

 mitral cusp ; p, posterior papillary muscle. Twice natural size. 



Fig. 12. Vertical transverse section of heart of dog in third stage of ventricular systole, to show occlusion of 

 tricuspid valve — letters as in 8. (From a drawing.) Natural size. 



Fig. 13. Vertical antero-posterior section of heart of rabbit in third stage of ventricular systole, to show con- 

 dition of left ventricle and mitral valve — letters as in fig. 11. SligMly enlarged. 



